Thank you for your response Per. I just wanted to know if option 2 is supported then we can go with it. Actually when transformed to Managed metadata column this field is working well for now. But who knows the future..!!!
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PguptaJun 22 '12 at 5:57

I am quite sure that your approach will not work fully. I have not heard of an approach where a taxonomy column can be correctly added to a content type by XML only. Have you for example tested your approach with search functionality and metadata navigation on a document library?

I would go with your approach 1 (or Per's) and make sure to add the taxonomy columns via code to your content types. That way you make sure that all aspects of the taxonomy colums will work properly.